Disc drives are the primary devices employed for mass storage of computer programs and data. Disc drives typically use rigid discs, which are coated with a magnetizable medium to form a recording layer in which data can be stored in a plurality of circular, concentric data tracks. Typical read/write heads include separate read and write head portions. One advantage to this configuration is that the read and write heads can be optimized for the particular task they perform.
The read head typically includes a magnetoresistive or giant magnetoresistive read element that is adapted to read magnetic flux transitions recorded to the tracks which represent the bits of data. The magnetic flux from the disc surface causes a change in the electrical resistivity of the read element, which can be detected by passing a sense current through the read element and measuring a voltage across the read element. The voltage measurement can be detected to determine the recorded data.
The write head includes an inductive recording element for generating a magnetic field that aligns the magnetic moments of the recording layer to represent the desired bits of data. Magnetic recording techniques include both longitudinal and perpendicular recording. Perpendicular recording is a form of magnetic recording which orients magnetic moments representing bits of data perpendicularly to the surface of the recording layer of the recording medium, as opposed to longitudinally along a track of the medium as in the more traditional longitudinal recording technique. Perpendicular recording offers advantages over longitudinal recording, such as significantly higher areal density recording capability.
Typically, the reader element is formed or fabricated as part of a wafer which is severed into a plurality of sliders. A magnetic writer is also integrated with the sensor during wafer fabrication. The slider carries reader elements and writer elements adjacent to the surface of the magnetic storage medium. The reader element and the writer are called the transducer, and the combination of the transducer and slider constitute what is called a magnetoresistive head. The slider of the magnetoresistive head is supported above the magnetic storage medium by the gimbal and the tongue of the load beam.
The head gimbal assembly may include a flex on suspension (FOS), a load beam, a mounting plate, a gimbal and the magnetoresistive head. The FOS extends from an actuator to a portion of the mounting plate, and is connected to the load beam. The load beam is also connected to the mounting plate. At the end of the FOS, the gimbal is connected to, and extends from, the FOS. Lastly, the gimbal is preferably coupled to the slider of the magnetoresistive head. The support arm, load beam and gimbal support and carry the magnetoresistive head adjacent a magnetic storage medium such as a magnetic disc.
The first and second electrical conductors electrically connecting the transducer and the detection circuitry typically comprise transducer leads and bonding pads. The transducer leads extend along a surface of the slider, are electrically connected to the bonding pads, and the bonding pads are connected to the transducer. The bonding pads provide a surface by which electrical conductors such as wire may be attached to electrically connected to the magnetoresistive head. The transducer leads further extend along the gimbal and the FOS to the detection circuitry. These leads can be carried on a flexible carrier substrate, such as polyimide.
Large currents or voltages associated with the charging or discharging of the transducer by electrostatic charge sources may possibly damage the reader element. Electrostatic charge may be generated any time during the fabrication, assembly, testing and shipment of the disc drive. Specifically, electrostatic charge may be generated during fabrication of the magnetoresistive head assembly, the head gimbal assembly, the E-block assembly, the final disc drive, electrical testing of components and shipment of the components. In response, various procedures and equipment have been installed to control electrostatic discharge (ESD) levels during every stage of handling through final disc drive assembly to prevent damage to the reader element caused by ESD. However, there are unique breakdown mechanisms associated with charge on the writer element of a transducer, which conventional ESD devices do not address. For instance, the sudden discharge of a writer terminal can generate damaging, transient currents through the reader element due to the capacitive and inductive coupling present between reader and writer. Additionally, it is likely that the use of bleed resistors connected only to the reader, shields and poles, when not paired with similar resistors connected to the writer coil, increase the risk of a particular transducer breakdown mechanism. If all terminals of a head are subjected to a charge source, the bleed resistors dissipate the charge only from the reader, shield and poles, and a voltage will be generated between the coils and poles that can cause failure. Thus there is a need for an ESD device that safeguards the recording head from sources subjecting both the reader and the writer to charging. The present invention addresses this need with the integration of writer bleed resistors, which effectively eliminate this failure mechanism.
Various means of reducing the risk of ESD damage to the reader exist. For example, in the field of FOS technology, the flex and covercoat material have been shown to highly tribochargable and thus a potential source for ESD damage to recording heads. Some prior systems have tried to minimize ESD by plating or covering the FOS with an intrinsically conductive polymer to minimize or eliminate potential charge-up of the FOS. However such systems are undesirable because there is a lack of contact between the conductive polymer and the electrical leads to the transducer. Other attempts to prevent ESD damage include applying anti-static coatings on the FOS, which lowers the surface resistivity. These coatings contaminate the drive environment and are therefore not desirable. Other techniques, such as a shunt clip or incorporating a diode on the suspension assembly for shunting, are not desirable to protect against ESD. The shunt clip and diode on the suspension assembly may not protect the reader element from ESD damage due to an inconsistent shunt and neglecting discharge from the writer element.
Therefore, there is a need for an ESD protection system that provides a consistent and secure connection with the transducer leads, that does not contaminate the drive environment and applies consistent resistivity to both the reader element and the writer element.
The present invention addresses these and other needs, and offers other advantages over current systems.